Sensor system in SiGe BiCMOS at 245 and 500 GHz for gas spectroscopy

This paper reviews our recent work on transmitter (TX) and receiver (RX) circuits in SiGe BiCMOS technology for gas spectroscopy in the frequency ranges around 245 GHz and 500 GHz. The 245 GHz TX consists of a 122 GHz local oscillator (LO) and a frequency doubler, and the 245 GHz RX consists of a low noise amplifier (LNA), a LO, and an active subharmonic mixer. A 245 GHz TX-array increases significantly the sensitivity of the sensor system. The 500 GHz system includes a TX-array, and a subharmonic RX with a transconductance mixer. The 500 GHz TX contains a frequency quadrupler, and the RX uses a frequency doubler for the LO. The LOs of the RX and the TX are controlled by two external phase-locked loops (PLLs). The reference frequency of the TX-PLL is frequency-modulated. The performance of the sensor system is demonstrated by using a gas absorption cell with dielectric lenses between the TX- and RX-modules, and measuring the 2f high-resolution absorption spectrum (second harmonic detection) of gaseous methanol (CH
₃
OH) and acetonitrile (CH
₃
CN).